Stan Wawrinka raced through his first outing since lifting the US Open title with comprehensive straight-sets win over Lukas Rosol at the St Petersburg Open.
Earlier this month Wawrinka claimed his third grand slam title at Flushing Meadows as he beat Novak Djokovic in four sets, and he looked to have maintained his fine form as he beat Rosol 6-3 6-1 on Wednesday.
Wawrinka's trademark backhand proved a deadly weapon against his Czech opponent, Rosol feeding the top seed's potent weapon far too often.
A backhand down the line gave Wawrinka his first break in the fifth game, and he followed it up in the ninth with another gain that gave him the opening set.
Rosol's challenge faded in the second set and Wawrinka took full advantage as he wrapped up victory in under an hour, converting his second match point.
Fellow seeds Joao Sousa, Viktor Troicki and Roberto Bautista-Agut also progressed to the quarter-finals, only Troicki progressing without dropping a set in his match with Gastao Elias.
Mikhail Youzhny and Andrey Kuznetsov gave the home fans plenty to cheer with victories over Janko Tipsarevic and Evgeny Donskoy respectively, while injury saw 2010 champion Mikhail Kukushkin retire in his clash with Andrey Rublev having been 6-3 4-1 behind.